Field sequential color encoding for displays

ABSTRACT

The optical performance is enhanced of display systems that use field sequential color and pulse width modulation to generate color and color gray scale values. Such enhancement may be achieved by various data encoding methods disclosed herein that may include temporal redistribution of bit values to mitigate color motional artifacts associated with field sequential color-based display systems, selective combination of intensity modulation, pulse width modulation, and/or the noncontiguous sequencing of primary colors. There is further an intelligent real-time dynamic manipulation of gray scale values in portions of an image that are computationally determined to be images of objects moving against a global background, so as to temporally front load or concentrate the bits comprising such moving objects and thereby further mitigate said motional artifacts using both actual and virtual aggregate pulse truncation across all primary colors being modulated.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/564,894 filed on Sep. 22, 2009, which claims priority to U.S.Provisional Patent Application No. 61/098,931 filed on Sep. 22, 2008,the entire disclosures of which are herein incorporated by reference.

TECHNICAL FIELD

The present application relates to the field of field sequential colordisplay systems, and more particularly to methods of encoding data tocontrol the data input to individual pixels of an array of pixels and/orto control the data input to illumination light sources for enhancingthe visual performance of field sequential color displays, whether in adirect-view display system or a projection-based display system.

BACKGROUND INFORMATION

This section is intended to introduce the reader to various aspects ofart that may be related to aspects of the present technique, which aredescribed and/or claimed below. This discussion is believed to behelpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presenttechnique. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

Data encoding methods or algorithms are utilized in electronic videodisplays, particularly with respect to flat panel display systems toselectively control the bursts of locally transmitted primary lightemitted from individual pixels disposed across the display surface. Oneexample for the application of such encoding algorithms is a direct-viewflat panel display system that uses sequentially-pulsed bursts of red,green, and blue colored light (i.e., primary colored light) emanatingfrom the display surface to create a sequence of primary color images,also referred to as primary color subframes, that integrated togetherform a full color image or frame by the temporal mixing of emittedprimary light that is being directed from the display surface to aviewer. A term commonly used to define this technique is called fieldsequential color (FSC). The human eye (i.e., human visual system) of theviewer effectively integrates the pulsed light from a light source toform the perception of a level of light intensity of each primary color(i.e., primary subframe).

In another aspect, the gray scale level generated at each pixel locationon the display surface is proportional to the percentage of time thepixel is ON during the primary color subframe time, tcolor. The framerates at which this occurs are high enough to create the illusion of acontinuous stable image, rather than a flickering one (i.e., anoticeable series of primary color subframes). During each primarycolor's determinant time period, t_(color), the shade of that primarycolor emitted by an individual pixel is controlled by encoding data thatselectively controls the appropriate fraction of t_(color) (i.e., amountof time) that the individual pixel is open during the time periodt_(color). A term commonly used to define this technique is called pulsewidth modulation (PWM). For example, producing 24-bit encoded colorrequires 256 (0-255) shades defined for each primary color. If one pixelrequires a 50% shade of red, then that pixel will be assigned with shade128 (128/256=0.5) and stay on for 50% of t_(color). This form of dataencoding assumes a constant magnitude light intensity from the lightsource that is modulated (i.e., pulse width modulated) across thedisplay screen by the selective opening and closing of individualpixels. Moreover, it achieves gray scales by subdividing t_(color) intofractional temporal components. An individual pixel that is open refersto the pixel in an ON state (i.e., light emitting), whereas anindividual pixel that is closed refers to the pixel in an OFF state(i.e., not light emitting). By making an array of pixels on a displayemit, or transmit, light in a properly pulsed manner (i.e., controllablyswitched between ON and OFF states), one can create a full-color FSCdisplay.

Various strategies for adjusting the color generation method for fieldsequential color-based display systems are geared either to theavoidance of solarization or posterization (linearity errors in creatinga true uniformly sloped monotonic gray scale relationship between inputand optical output of a display at any given point) and motional colorbreakup artifacts related to the temporal decoupling of the variousprimary frames comprising an image when they arrive at the retina, suchthat an object noticeably decomposes into its constituent primarycomponents since those components no longer properly overlap as aconsequence of relative retina-object motion during the viewing of thedisplay. However, these various strategies induce engineeringcompromises since the response time of various pixel architectures maybe either marginal or inadequate to generate both adequate gray scaleand incorporate the artifact mitigation strategies proposed to correctfor the kind of imaging errors just described. The larger a displaysystem, or the higher its pixel density, the greater this gap betweenresponse requirements and minimal performance to deploy motional colorbreakup mitigation strategies becomes. However, the display industrycontinues to evolve toward larger, higher-density display systemsbecause of growing industrial, military, and commercial needs in regardto information display. Because these issues have yet to besatisfactorily addressed in regard to motional color breakup inparticular, the prior art has fallen short in respect to presenting aworkable solution to this ongoing problem in display technology.

SUMMARY

The problems outlined above may at least in part be solved in someembodiments of the methods described herein. The following presents asimplified summary of the disclosed subject matter in order to provide abasic understanding of some aspects of the disclosed subject matter.This summary is not an exhaustive overview of the disclosed subjectmatter. It is not intended to identify key or critical elements of thedisclosed subject matter or to delineate the scope of the disclosedsubject matter. Indeed, the disclosed subject matter may encompass avariety of aspects that may not be set forth below. Its sole purpose isto present some concepts in a simplified form as a prelude to the moredetailed description that is discussed later.

The embodiments of the present disclosure provide various data encodingmethods that reduce motional color breakup native to field sequentialcolor displays. Some of the embodiments also provide a means to reducedemands on pixel response speeds. A first embodiment of the presentdisclosure is a method including modulating an intensity of theillumination means of the display system in tightly-coordinatedconjunction with the temporal modulation of the pixel actuationsequence. A second embodiment of the present disclosure is a methodincluding hard-wired front-loaded bit weighting to enhance perceivedmitigation of motional artifacts using virtual aggregate pulse widthtruncation. A third embodiment is a method including bit-splitting todivide higher order bits (such as the most significant bit (MSB)) whichhave the longest temporal duration, into smaller subunits that may bedistributed and interleaved (i.e., intermixed) for all three stimuluscolors. Bit-splitting across all three tristimulus colored lights may becombined with the principle of intensity modulation of the illuminationsource disclosed in the first embodiment. A fourth embodiment is amethod including distributing pulse-width-modulated temporal pulses soas to average out the relative bit weights over the entire tristimulussequence comprising a full color frame, thereby interleaving the varioustristimulus components to provide the best image quality as empiricallydetermined by actual visual performance of such systems. A fifthembodiment is a method including distributing pulse-width-modulatedtemporal pulses so as to front-load all the most significant bitsrelative to the specific single video frame being generated. Thisembodiment hardwires the bit sequence from the most significant bits ofall three primaries being encoded first, followed by the next mostsignificant bits of all three primaries, and so on down to the leastsignificant bits. A sixth embodiment is a method including real-timeevaluation of each video frame being generated to determine theparticular rearrangement of the bits to be displayed. In contrast to thehardwired bit sequence of the fifth embodiment, the sixth embodimentdynamically adjusts the bit sequence in light of the exigencies of eachframe's program content, thereby insuring that the correct bits aretruly weighted to the front of the aggregate pulse being encoded acrossall primaries. A seventh embodiment is a method including determining ina received plurality of video frames that an object to be displayed in aforeground of a video image is in motion relative to a background of thevideo image, and modifying a gray scale of the video frames associatedwith the object to be displayed in the foreground of the video image.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features, aspects, and advantages of the present invention willbecome better understood when the following detailed description is readwith reference to the accompanying figures in which like charactersrepresent like parts throughout the figures, wherein:

FIG. 1 illustrates a temporal breakdown of binary-weighted consecutiveorder bits for a single primary color according to conventional pulsewidth modulation methods to secure gray scales at a bit depth of 8,representing 256 different brightness levels from black to white,generated within 1/180 of a second, with blackout (blanking) periodsbetween each bit level omitted;

FIG. 2 illustrates a concatenation of three consecutive 8-bit gray-scaleunits of 1/180^(th) of a second in duration such as shown in FIG. 1,with the first block representing one tristimulus color (e.g., red), thesecond block representing the second tristimulus color (e.g., green),and the third block representing the third tristimulus color (e.g.,blue), such that the entire temporal period shown of 1/60^(th) of asecond duration represents the switching template required to generatefull color images on a display at a total color bit depth of 24(approximately 16.7 million colors);

FIGS. 3A-3F compare the original temporal subdivision of a singleencoded primary color depicted in FIG. 3A (previously shown in FIG. 1)with: FIG. 3B which illustrates an intensity-modulated equivalent thatelects to truncate total duration of the primary color pulse bypostpositing the accrued time savings, and FIG. 3C which illustrates analternate intensity-modulated equivalent that elects to redistribute thetime saved over all relevant bits to reduce addressing overhead timesintrinsic to the high speed operation of field sequential color-baseddisplay systems, and FIG. 3D which illustrates the aggregate pulseencoding for all three tristimulus primaries (as previously shown inFIG. 2), and FIG. 3E which illustrates an intensity-modulated variationthat extends the principle of FIG. 3B to all three primaries in the fullcolor encoded packet, and FIG. 3F which illustrates actual noncontiguousinterleaving of the respective primary bits weighted such that thehigher order bits appear earlier in the aggregate full color sequence ofpulses, and FIG. 3G which illustrates the conflating of intensitymodulation and actual noncontiguous interleaving of the respectiveprimary bits weighted such that the higher order bits appear earlier inthe aggregate full color sequence of pulses;

FIG. 4A illustrates a subset of the pulse width modulated durations fora single primary color shown in FIG. 1, namely, the four highest orderbits, omitting the four lowest order bits for illustrative purposes;

FIG. 4B illustrates the splitting of the durations for a single primarycolor shown in FIG. 4A into fractional subdivisions bearing the sameduration as the smallest illustrated bit width, without anyrearrangement of the bits in terms of sequence;

FIG. 4C illustrates the rearrangement of the split bits for a singleprimary color previously shown without rearrangement in FIG. 4B suchthat the higher order bits are distributed as evenly as possible overthe entire duration of the primary color generation time;

FIG. 5A illustrates the full color cycle for all three primary colors asformerly shown in FIG. 3E with intensity modulation applied to thesequence, with only the four highest order bits being annotated in thefigure;

FIG. 5B illustrates the mixing of several levels of intensity modulationand pulse width modulation as applied only to the four highest orderbits for the entire color cycle comprised of all three primary colors;

FIG. 5C illustrates the interleaving of the various intensities andpulse widths shown in FIG. 5B so as to best average out the intensityfor any given primary color across the entire aggregate pulse durationfor the entire three-primary video frame being displayed;

FIG. 5D illustrates the hard-wired interleaving of the variousintensities and pulse widths shown in FIG. 5B so as to force all thehighest order bits, regardless of program content, to be displayed atthe beginning of the aggregate pulse comprising the video frame for allthree primary colors;

FIG. 5E illustrates one possible result due to real-time analysis ofeach video frame to determine which bits are most important based onimage content, therefore making the frame-to-frame sequence of theintensities and pulse widths to be dynamically variable based on theimage content of the frame being displayed;

FIG. 6 sets forth a method for dynamically altering the gray scale depthfor regions of the video display that are contextually shown, accordingto real-time analysis of consecutive frames within the display system'svideo cache, to represent foreground objects in relative motion againstthe perceived background, such that if a detectable threshold formotional artifact generation is crossed by such motion, the movingforeground object is posterized and/or quantized to permit maximumfront-loading of image data during the full three-primary color pulsedisplaying the frames in question;

FIG. 7 illustrates a perspective view of a direct view flat paneldisplay suitable for implementation of the present invention;

FIG. 8A is a side view schematic of a single pixel in an OFF state;

FIG. 8B illustrates the pixel shown in FIG. 8A in an ON state;

FIG. 9A is a side view schematic of a single pixel in an OFF state,wherein the pixel has collector-coupler features;

FIG. 9B illustrates the pixel shown in FIG. 9A in an ON state;

FIG. 10 illustrates what causes the phenomenon of color image breakupwhen an observer views an image generated using field sequential colorgeneration techniques during rotational motion of the observer's eye;

FIG. 11A illustrates the perceived image that is desired irrespective ofeye rotation and/or other motion in accordance with an embodiment of thepresent invention; and

FIG. 11B illustrates the phenomenon of color image breakup by depictinga perceived image due to eye rotation and/or other motion.

DETAILED DESCRIPTION

Among the technologies (flat panel display or other candidatetechnologies that exploit the principle of field sequential colorgeneration) that lend themselves to implementation of the presentdisclosure is the flat panel display disclosed in U.S. Pat. No.5,319,491, which is hereby incorporated herein by reference in itsentirety. The use of a representative flat panel display examplethroughout this detailed description shall not be construed to limit theapplicability of the present invention to that field of use, but isintended for illustrative purposes as touching the matter of deploymentof the present invention. Furthermore, the use of the three tristimulusprimary colors (red, green, and blue) throughout the remainder of thisdetailed description is likewise intended for illustrative purposes, andshall not be construed to limit the applicability of the presentinvention to these primary colors solely, whether as to their number orcolor or other attribute.

One possible display technology to be enhanced (without therebyrestricting the range of applicability of the present invention) may bethe current iteration of the display technology originally disclosed inU.S. Pat. No. 5,319,491, wherein pixels emit light using the principleof frustrated total internal reflection within a display architecturethat leverages principles of field sequential color generation and pulsewidth modulated gray scale creation. In that display system, light isedge-injected into a planar slab waveguide and undergoes total internalreflection (TIR) within the guide, trapping the light inside it.Edge-injected light may comprise any number of consecutive primarycolored lights, for example three primary colored lights (also referredto as tristimulus primaries), synchronously clocked to a desirableglobal frame rate (e.g., 60 Hz, requiring a 180 Hz rate to accommodateeach of the three primaries utilized therein, namely, red, green, andblue). Pixels are electrostatically controlled MEMS structures thatpropel a thin film layer, hereinafter termed the “active layer”, whichis controllably deformable across a microscopic gap (measuring between300 to 1000 nanometers) into contact or near-contact with the waveguide,at which point light transits across from the waveguide to the activelayer either by direct contact propagation and/or by way of evanescentcoupling. In other words, application of an appropriate electricalpotential across the gap, with conductors associated with the slabwaveguide and the active layer to be propelled/deformed, causes thehigh-speed motion of the active layer toward the slab waveguide;actuation is deemed completed (i.e., ON state) when the active layer canmove no closer to the slab waveguide (either in itself, or due tophysical contact with the slab waveguide). The active layer in contact(or near contact) with a surface of the waveguide optically coupleslight out of the waveguide thereby extracting light from the waveguidevia frustration of total internal reflected light (FTIR). The FTIR lightextracted by the active layer may be directed towards a viewer asemitted light at that pixel location.

The flat panel display is thus comprised of a plurality of pixels, eachpixel representing a discrete subsection of the display that can beindividually and selectively controlled in respect to locally propellingthe active layer bearing a suitable refractive index across amicroscopic gap between ON and OFF positions thereby switching theindividual pixel between ON and OFF states. FIG. 7 illustrates asimplified depiction of a flat panel display 700 comprised of awaveguide (i.e., light guidance substrate) 701 which may further includea flat panel matrix of pixels 702. Behind the waveguide 701 and in aparallel relationship with waveguide 701 may be a transparent (e.g.,glass, plastic, etc.) substrate 703. It is noted that flat panel display700 may include other elements than illustrated such as a light source,an opaque throat, an opaque backing layer, a reflector, and tubularlamps (or other light sources, such as LEDs, etc.).

A principle of operation for any of the plurality of pixels distributedacross the slab waveguide involves locally, selectively, andcontrollably frustrating the total internal reflection of light boundwithin the slab at each pixel location by positioning the active layer,into contact or near contact with a surface of the slab waveguide duringthe individual pixel's ON state (i.e., light emitting state). To switchthe individual pixel to its OFF state (i.e., light is not emitted atthat pixel location), the active layer is sufficiently displaced fromthe waveguide by a microscopic gap (e.g., an air gap) between the activelayer and the surface of the waveguide such that light coupling andevanescent coupling across the gap is negligible. The deformable activelayer may be a thin film sheet of polymeric material with a refractiveindex selected to optimize the coupling of light during thecontact/near-contact events, which can occur at very high speeds inorder to permit the generation of adequate gray scale levels formultiple primary colors at video frame rates in order to avoid excessivemotional and color breakup artifacts while preserving smooth videogeneration.

For example, FIGS. 8A and 8B illustrate a more detailed side view of onepixel 702 in an OFF and ON states, respectively. FIG. 8A shows anisolated view of a pixel 800, in an OFF state geometry, having an activelayer 804 disposed in a spaced-apart relationship to a waveguide 803 bya microscopic gap 806. Each pixel 800 may include a first conductorlayer (not shown) in or on a waveguide 803, and a second conductor layer(not shown) in or on the active layer 804. The pixel 800 is switched toan ON state, as depicted in FIG. 8B, but applying a sufficientelectrical potential difference between the first and second conductorlayers that causes the active layer 804 to deform and move towards asurface of the waveguide such that the active layer couples light out ofthe waveguide as illustrated by emitted light ray 808. However, theremay be a certain amount of light loss due to the presence of reflectedlight rays 810, 812, and 814. To minimize the amount of reflected light,a plurality of collector-coupler features 903 may be disposed on a lowersurface of the active layer 902, as depicted by pixel 900 in OFF and ONstates illustrated in FIGS. 9A and 9B, respectively. When the pixel 900is in the ON state (FIG. 9B), the collector-coupler features 903interact with light waves 912 that approach the vicinity of thewaveguide-active layer interface, increasing the probability of lightwaves to exit the waveguide and enter the active layer 902 and directingemitted light 910 towards a viewer. Since light is coupled out of thewaveguide by the collector-coupler features 903, an opaque material 904can be disposed between the collector-coupler features 903. The opaquematerial 904 prevents light from entering the active layer 902 atundesired locations, improving overall contrast ratio of the display andmitigating pixel cross-talk. The opaque material 904 can substantiallyfill the interstitial area between the collector coupler features 903 ofeach pixel, or it can comprise a conformal coating of these features andthe interstitial spaces between them. The aperture 908 of eachcollector-coupler 903 remains uncoated so that light can be coupled intothe collector-coupler 903. Depending on the desired use of the display,the opaque material 904 may be either a specific color (e.g., black) orreflective.

The use of a representative flat panel display example throughout thisdetailed description shall not be construed to limit the applicabilityof the present invention to that field of use, but is intended forillustrative purposes as touching the matter of deployment of thepresent invention. Furthermore, the use of the three primary colors(red, green, and blue) throughout the remainder of this detaileddescription is likewise intended for illustrative purposes, and shallnot be construed to limit the applicability of the present invention tothese primary colors, whether as to their number or color or otherattribute.

As stated previously, certain field sequential color displays, such asthe one illustrated in FIG. 7, exhibit undesirable visual artifactsunder certain viewing conditions and video content. The cause of suchharmful artifacts proceeds from relative motion of the observer's retinaand the individual primary components of a given video frame during thesuccessive transmission in time of each respective subframe primarycomponent. The display of FIG. 7 serves as a pertinent example that willbe used, with some modifications for the purpose of generalization,throughout this disclosure to illustrate the operative principles inquestion. It should be understood that this example is provided forillustrative purposes as a member of a class of valid candidateapplications and implementations, and that any device, comprised of anysystem exploiting the principles that inhere in field sequential colorgeneration, can be enhanced with respect to artifact reduction orsuppression where said artifacts stem from the primary componentscomprising a video frame falling on different geometric regions of theobserver's retina due to relative motion of retina and display.

FIG. 10 illustrates in accordance with an embodiment of the presentdisclosure the general phenomenon of color image breakup in FSCdisplays. The information being displayed on the display surface duringa given video frame proceeds to the observer's retina 1009 as a seriesof collinear pulses 1001 and 1005 comprised of the respectiveconsecutively-generated primary information constituting each videoframe. So video frame information for a frame 1001 is composed oftemporally separated primaries 1002, 1003, and 1004, while another videoframe 1005 (one frame prior in time to frame 1001) is likewise composedof temporally separated primaries 1006, 1007, and 1008. The informationcontained as an array of pulse width modulated colored light for eachprimary color arrives at the retina 1009 to form an image. If theprimary subcomponents 1006, 1007, and 1008 arrive at the same locationon the retina, the eye will merge the primaries and perceive a compositeimage without any color breakup. However, if the retina 1009 is inrotational motion, then the phenomenon at the retina follows the patternof video frame 1010, where the individual primary components 1011, 1012,and 1013 fall on different parts of the retina, causing the colorbreakup artifact to be perceptible.

FIGS. 11A and 11B illustrate the intended image depicted in FIG. 11A ascompared to the actual perceived image depicted in FIG. 11B. Forexample, if the primary components comprising video frame 1010 allarrived at the same location on the retina, the eye would merge theprimary subframes to accurately form the composite image 1000, which inthis example is an image of a gray airplane. However, if the eye is inrotational motion, retina 1009 moves with respect to the consecutiveprimary colored images (i.e., primary subframes) comprising video frame1010, such that 1011, 1012, and 1013 (the primary components comprisingthe entire frame 1010) fall at different locations on retina 1009,resulting in the perceived image 1102, where the separate primarycomponents 1103, 1104, and 1105 are perceived no longer as fullyoverlapping, but rather distributed across the field of view in adissociated form, as shown. Recovery of the intended image 1101 is thegoal of artifact suppression, whereby the splayed, dissociated image1102 is reduced or suppressed by virtue of extirpation of the cause ofsuch dissociation.

Color display systems that utilize a temporally-based color generationmethod may require the means to mitigate, suppress, and control motionalartifacts arising from the temporal decoupling of the primary colorconstituents comprising an image due to these constituents arriving atdifferent points on the observer's retina due either to rotary motion ofthe eye or to the eye's tracking of a foreground object in the videoimage that is in motion relative to the perceived background of thatimage. The various embodiments of the present disclosure provideencoding methods to mitigate color breakup motional artifacts and/orreduce demands on pixel response speeds. The present invention may beimplemented on a host of display systems (direct view orprojection-based) that could be expected to use field sequential colorencoding techniques and thus would be highly desirable and lead toimproved image generation by system architectures based on the fieldsequential color paradigm.

To provide a better understanding of the encoding methods of the presentdisclosure, FIG. 1 illustrates the conventional breakdown of a singleprimary color into pulse width modulated constituents that stand inbinary proportions one to another. The three tristimulus primary coloredlights used in field sequential color displays are red, green, and blue,and displays using field sequential color use at least these threeprimaries for image generation. A conventional frame rate for videoframes in such displays is 60 frames per second (60 fps) for all threecolors, which means that one-third of this time period of 1/60th of asecond is allocated to each of the tristimulus primaries: 1/180^(th) ofa second for red, for green, and for blue, totaling 1/60^(th) of asecond. FIG. 1 illustrates one of these primary colored light (e.g.,red) and its duration, referred to as a primary pulse duration 100, andhow it is further subdivided into smaller fractions. For 8-bit color,which provides 2⁸ different intensities or gray scale levels for theprimary color (256 gray scales), it is appropriate to subdivide theentire pulse of 1/180^(th) second into eight fractions referred to asbits 101, 102, 103, 104, 105, 106, 107, 108. Wherein, the second bit 102is a second subdivision lasting ½ the primary pulse of bit 101 (i.e.,the first subdivision), the third bit 103 is a third subdivision lasting¼ the primary pulse of bit 101, the fourth bit 104 is a fourthsubdivision lasting ⅛ the primary pulse of bit 101, the fifth bit 105 isa fifth subdivision lasting 1/16 the primary pulse of bit 101, the sixthbit 106 is a sixth subdivision lasting 1/32 the primary pulse of bit101, the seventh bit 107 is a seventh subdivision lasting 1/64 theprimary pulse of bit 101, and the eighth bit 108 is an eighthsubdivision lasting 1/128 the primary pulse of bit 101. In other words,the duration of each bit 102 through 108 is a consecutive halving of theprevious bit, wherein bit 108 represents 1/256 of the original primarypulse duration also referred to an aggregate primary pulse 100. Any oneof 256 different values of intensity based on pulse width modulation(the amount of time light is allowed to pass through any given pixelbeing independently modulated according to this schema) can be generatedby appropriate actuation of the pixel to either an ON or OFF stateduring the eight time periods of bits 101 through 108. If a given pixelis OFF for all eight time periods, the gray scale level being displayedfor that pixel is zero (no intensity of the given primary), and if thepixel is ON (i.e., open) for all eight subdivisions, the intensity ismaximized for the pixel being so actuated. By setting the temporalsubdivisions in consecutive 2-to-1 binary relationships, the encoding ofdigital information in temporal form to generate gray scale values viaPWM is made particularly efficient from the standpoint of driveelectronics exigencies, especially as compared to subdividing the1/180^(th) aggregate full pulse 100 into 256 evenly-dividedsubdivisions, which requires 32 times as many addressing cycles as istaught in FIG. 1. The horizontal axis represents time passing from leftto right, while the vertical axis represents the intensity of theillumination source (i.e., light source) feeding at least one (if notall) pixels being actuated according to the principles of displayoperation to enable field sequential color image generation.

FIG. 2 illustrates how the three consecutive primaries (of 1/180^(th)second duration each) are arrayed sequentially, one after another, toform a full color video frame of 1/60^(th) of a second duration (i.e.,1/180^(th) of a second per color primary multiplied by three total colorprimaries being modulated) in a conventional FSC display. A firstprimary color that lasts for a primary pulse duration 100 a has an 8-bitgray scale decomposition as previously shown by the single primary colorlight that lasts for a primary pulse duration 100 in FIG. 1. The firstprimary color represented by duration 100 a may be the color red,although the present invention need not be tied to any one of the sixpossible combinations of the three tristimulus primaries that provideillumination to the pixels (which are turned on or off (i.e., switchedbetween ON and OFF states) according to the requirements of the colorframe as encoded according to the sequence of bits for each primaryshown in FIG. 2). The first primary pulse duration 100 a is followed bya second primary pulse duration 100 b that illuminates a different color(e.g., green) for an identical duration of 1/180^(th) of a second, and athird primary pulse duration 100 c that illuminates a different color(e.g., blue) for an identical duration of 1/180^(th) of a second. Theconsecutive sequential series of tristimulus primaries (i.e., threeprimary colored light) and their possible binary subdivisions isreferred to as an aggregate tristimulus pulse 200. Because in theexample shown each primary color is subdivided into 8 bits (256 possiblegray scales), the aggregate color capability for this example is 24-bitcolor (over 16.7 million possible colors based on the gray scalesavailable for each of the three tristimulus primaries of red, green, andblue).

In the two examples illustrated in FIGS. 1 and 2, there is no attempt tomodulate the intensity of the illumination sources feeding the displaysystem. All gray scales are generated solely by temporal considerations:the pulse width modulation of light flux by way of pixel actuation anddeactuation is adequate to create and control digital gray scale valuesindependently at each pixel for a suitably configured display system. Inanother aspect, it should be noted that blanking periods may be insertedbetween each of the subdivisions to accommodate driver timing issues(e.g., to load the pixel data) and illumination transient responseissues to insure linearity of response, but these possible blankingstates (where the illumination means are briefly shut off at theboundaries between individual gray scale bits, or between consecutiveprimary colors being displayed) are omitted in the figures of thepresent disclosure since their possible inclusion is assumed as likely,without thereby being necessarily an intrinsic part of the presentdisclosure and its diverse methods for meeting the existing needs in theart to mitigate motional artifacts and/or relax pixel response timerequirements. The methods of the present disclosure are applicablewhether or not such blanking periods are present.

In a first embodiment, modulating an intensity of the illumination meansof the system in tightly-coordinated conjunction with the temporalmodulation of the pixel actuation sequence permits either (a) truncationof the aggregate pulse defining any given primary color full-lengthframe (all bits accounted for), such that by asynchronous distributionthe entire series of tristimulus pulses would be thereby truncated tomitigate motional artifacts, or (b) said sequence permits distributionof the time gained (by using such synchronized intensity modulationwithin the illumination system as a surrogate for temporal duration forthe most significant bits) amongst all bit durations comprising thetotal gray scale makeup of the full primary frame so as to relax thetransient response requirements upon the pixels at the heart of thedisplay architecture. Further, a combination of these two desirableeffects (temporal truncation and reduced demands upon pixel speed) isalso possible under this embodiment.

In particular, the first embodiment provides a method for combiningintensity modulation with PWM to achieve aggregate pulse truncation tomitigate color motional breakup artifacts, as illustrated in FIG. 3B, orto relax pixel transient response requirements as illustrated in FIG.3C. For comparison purposes, FIG. 3A again displays the fundamentalpulse 100 as previously depicted in FIG. 1, showing that the entirepulse of the primary color has an overall duration of 1/180^(th) of asecond. It is possible, however, to shorten the amount of time that theprimary color is displayed. Shortening of the display time for a givengray scale value, which serves to truncate the pulse, is a valuable toolfor mitigating the effects of motional color breakup. The temporaldecoupling of the constituent primaries comprising an image generated ona field sequential color display can be reduced when the varioustemporal components of the frame arrive closer together in time (due toaggregate pulse truncation). The means of shortening the display timewithout affecting the desired flux being displayed by any given pixelinvolves amplitude modulation of the intensity being displayed through agiven pixel. By setting up the FSC system so that the globalillumination means operates at, for example, double its normal intensityduring the most significant bit being displayed, the pulse width of thatmost significant bit can be halved without affecting its luminous flux.The most significant bit 101 in the non-intensity-modulated primarypulse shown in FIG. 3A becomes truncated in FIG. 3B as bit 301. Bits102, 103, 104 through 108 of FIG. 3A therefore become bits 302, 303, 304through 308 of FIG. 3B. These latter seven bits (i.e., pulses) areunchanged; however, the first pulse of the full set of eightsubdivisions, i.e., the most significant bit 101 of FIG. 3A, now becomesbit 301 of FIG. 3B that exhibits half the temporal duration but doublethe intensity of the global illumination system feeding the pixelscomprising the display. The area of bit 101 in FIG. 3A and the area ofbit 301 in FIG. 3B are identical, and this area (representing theproduct of intensity and time) represents the perceived intensity of thepulse based on total light flux passing through the pixel(s) inquestion. Note, however, that with the halving of the duration of bit101 (such that the temporal of duration of bit 301 is now equal to thatof bit 302, rather than twice the duration of bit 302 as would have beenrequired had intensity modulation not been integrated with pulse widthmodulation), there is extra time available for the overall primary pulseto be encoded, this extra time is referred to as a time savings 310. Inthis example, the time savings 310 is equal to the duration of bit 302(which is equivalent to the time duration of bit 102 in FIG. 3A). Thissaved time 310 may be used to truncate the aggregate pulse. In FIG. 3B,the overall pulse is shortened by the duration of time savings 310.Truncation of the aggregate pulse for any one or more of the primarycolor full-length frames (e.g., each of the primary pulses of light;red-green-blue) may be employed such that each of the tristimulus pulseswould be thereby truncated to mitigate motional artifacts.

Alternatively, FIG. 3C illustrates that the additional time provided bytime savings 310 is not used to shorten the aggregate pulse and createdead space after 308 as displayed in FIG. 3B, but rather, the durationof the time savings 310 may be equally distributed among all eightbinary subdivisions 311 through 318. This may be appropriate where thespeed of pixel response becomes a factor in displaying the leastsignificant bits (shortest pulse durations) required to generate certaingray scale values. In the case of FIG. 3C, the primary color beingdisplayed (e.g., red) is just as long as was displayed in FIG. 3A, butthe timing demands on the pixels are relaxed because intensitymodulation of the most significant bit 311 has bought the system someextra safe operating area in regard to temporal demands upon the pixelshuttering mechanisms native to the display architecture in question.Whereas displays that do not have the temporal demands, the dynamicrange of the light output will increase due to the resulting increase ofoverall pixel intensity.

It should be noted that intensity modulation as shown in FIGS. 3B and 3Cis not limited to simply doubling the intensity for the most significantbit 301, 311. One could just as easily quadruple the intensity for themost significant bit 301, 311 and double the intensity for the next mostsignificant bit 302, 312, thereby gaining even greater temporal gains,which can either translate to a shorter overall pulse duration for all 8bits (as sought in FIG. 3B) or further reduce high speed actuationrequirements on the pixels (as implemented in FIG. 3C). This embodimentallows for any level of coordinated segmentation between controlledintensity modulation and pulse width modulation to secure the correctbinary proportions of net flux reaching the observer's retinas whileviewing the display being so enhanced.

For comparison purposes, FIG. 3D again illustrates the entirethree-primary frame of 1/60^(th) second duration, as previously depictedin FIG. 2, capable of exhibiting an aggregate total color bit depth of24 bits (i.e., 8 bits per primary multiplied by three tristimulusprimary colors (denoted by lower case “a”, “b”, and “c”) being modulatedsequentially in time. First primary pulse duration 100 a, second primarypulse duration 100 b, and third primary pulse duration 100 c wouldrepresent, for example, the respective red, green, and blue temporalsubframes of 1/180^(th) second each duration comprising the entire fullcolor frame 200 in FIG. 3D. When intensity modulation is applied to allthree primary colored lights a, b, c comprising the full color frame, asin FIG. 3E, the durations (i.e., pulse widths) of most significant bits301 a, 301 b and 301 c are halved in duration, as compared to 101 a, 101b, and 101 c depicted in FIG. 3D, so that the respective total primarypulse durations 300 a, 300 b and 300 c are individually truncated andthus truncated in the aggregate, with the time savings by a durationreferred to as a time savings 320 depicted in FIG. 3E. As illustrated inthis example, the time savings 320 is equal to three times the durationof pulse 302 a. This time savings 320 may be utilized as a blankingperiod during which black is displayed to reduce decoupling of theprimary components as they fall on the observer's retina.

A second embodiment of the present disclosure provides a method tocreate hard-wired front-loaded bit weighting to enhance perceivedmitigation of motional artifacts using virtual aggregate pulse widthtruncation. As illustrated in FIG. 3F, the temporal rearrangement of thevarious bit weights comprising the total aggregate color gray scale tobe produced by a given pixel during a full frame can be conducted alonglines geared toward favoring the front-loading of the most significantbits 101 a, 101 b, and 101 c corresponding to each of the primarycolored lights a, b, c, as compared to the embodiment previouslydescribed with respect to FIG. 3D wherein the most significant bits 101a, 101 b, and 101 c are distributed in separate first, second, and thirdprimary pulse durations 100 a, 100 b, and 100 c respectively. Combiningbit-rearranging with non-contiguous primary processing, as illustratedin FIG. 3F, may position the same bit weights for each of the threeprimary colors (a, b, c), contiguous with one another thereby forming afirst triplet 322 of all three most significant bits 101 a, 101 b, 101c. Likewise, the second most significant bits 102 a, 102 b, 102 c aresimilarly aggregated as a second triplet 324, the third most significantbits 103 a, 103 b, 103 c are similarly aggregated as a third triplet326, the fourth most significant bits are similarly aggregated as afourth triplet 328, the fifth most significant bits are similarlyaggregated as a fifth triplet 330, the sixth most significant bits aresimilarly aggregated as a sixth triplet 332, the seventh mostsignificant bits are similarly aggregated as a seventh triplet 34, andthe eighth most significant bits (i.e., least significant bits) aresimilarly aggregated as an eighth triplet 336, representing eachdescending bit weight being encoded according to the binary weightingparadigm defined at the outset. A display system must be capable ofdisplaying bits in such a sequence, including a noncontiguous primarycolor light a, b, c processing sequence (where noncontiguous would bedefined as a sequence violating the standard red-green-blue or similarsequential illumination of the display system to provide light to thematrix of pixels on the display surface). In this embodiment, there isno attempt to modulate the intensity of the illumination sources feedingthe display system. All gray scales are generated solely by temporalmeans such as pulse width modulation of light flux by way of pixelactuation and deactuation. PWM is adequate to create and control digitalgray scale values independently at each pixel for a suitably configureddisplay system.

As shown in FIG. 3G as compared to FIG. 3E, the temporal rearrangementof the various bit weights comprising the total aggregate color grayscale to be produced by a given pixel during a full frame can beconducted along lines geared toward favoring the front-loading of themost significant bits. Whereas in FIG. 3E, the most significant bits 301a, 301 b, and 301 c are distributed in separate first, second, and thirdprimary pulse durations 300 a, 300 b, and 300 c, respectively, in theembodiment illustrated in FIG. 3G the same bit weights are contiguouswith one another, forming a first triplet 322 of all three mostsignificant bits 301 a, 301 b, 301 c. The second most significant bits302 a, 302 b, 302 c are similarly aggregated as a second triplet 324,the third most significant bits representing a third triplet 326, thefourth most significant bits representing a fourth triplet 328, and soon such that the fifth, sixth, seventh and eighth most significant bitsare rearranged into fifth, sixth, seventh, and eighth triplets 330, 332,334, 336 representing a triplet for each descending bit weight beingencoded according to the binary weighting paradigm defined at theoutset. A display system must be capable of displaying bits in such asequence, including a noncontiguous primary color light processingsequence mitigates motional artifacts native to field sequential colordisplay systems. In subsequent embodiments it will be noted thatmanipulation of such color sequences becomes an important adjunct tomitigating motional color artifacts, particularly where the transientresponse of the pixels is already near their performance limits.

In a third embodiment, bit-splitting is deployed to divide higher orderbits (e.g., the most significant bit (MSB) 101), which have the longesttemporal duration, into smaller subunits that total the duration of theoriginal pulse of MSB 101. The split bits may be distributed andinterleaved for all three stimulus colors a, b, c, which are thusintermixed (unlike prior art bit-splitting which is limited tobit-splitting within a single primary due to the exigencies of colorwheel operation native to the displays incorporating such techniques).FIG. 4A illustrates the four most significant bits 101, 102, 103, and104 of the original primary color binary weighting paradigm set forth inFIG. 1. FIG. 4B illustrates how the larger, more significant bits (e.g.,bits 101, 102, 103 illustrated in FIG. 4A) can be subdivided. In thisexample, bits 101, 102, and 103 are all subdivided into multiples of theduration set for the fourth most significant bit 104, as shown in FIG.4B. The value of bit splitting as a method is not properly realizeduntil the bits forming the single primary color gray scale arerearranged, such as illustrated in FIG. 4C, which attempts to provide anaveraged weighting of each of the respective bit weights across theentire 1/180^(th) of a second for the single primary color pulseduration 100. In FIGS. 4B and 4C, there are eight fractional durations101′ comprising the most significant bit 101, four fractional durations102′ comprising the second most significant bit 102, two fractionaldurations 103′ comprising the third most significant bit 103, and onlyone duration 104 comprising the fourth most significant bit 104. Thelower order bits (bits 105, 106, 107, and 108) are omitted for the sakeof illustrative clarity, although they would arguably be handled in asimilar fashion according to this method.

In this third embodiment, bit-splitting across all three tristimuluscolors may be combined with the principle of intensity modulation of theillumination source disclosed in the first embodiment to secure superioroptical performance while gaining either (a) additional aggregate pulsewidth truncation to further mitigate motional artifacts, (b) distributeany time saved due to the addition of intensity modulation among allbits being temporally generated to reduce the demand on pixel speeds inthe display architecture, or (c) a combination of both motional artifactmitigation and reduction of pixel response requirements.

An embodiment of the present invention teaches the coordinatedmodulation of light source intensity with pulse width modulation tofacilitate aggregate pulse width truncation. FIG. 5A reproduces theprimary time savings already disclosed in FIG. 3E, while FIG. 5B (forthe sake of clarity) omits the four lowest order bits to set forth avariation on an intensity-modulated method as applied to the fourhighest order bits, namely 301 a, 302 a, 303 a, and 304 a. Note that thearea of each of these respective bit weights represents the potentialflux that can be generated by any given pixel in question (if the pixelwere turned on for all such segments the flux would be actual). In FIG.5B, note that the respective primaries are still treated contiguously,such that 300 a represents one primary color light pulse being modulatedby intensity and pulse width modulation, and 300 b and 300 c representthe other two primary colored lights.

A fourth embodiment is a method that may include combining intensitymodulation with PMW to create averaged primary weights across theaggregate full color three primary frame duration via noncontiguousprimary colored light sequencing. The fourth embodiment of the presentdisclosure distributes conventional pulse-width-modulated temporalpulses so as to average out the relative bit weights over the entiretristimulus primary color sequence comprising a full color frame,thereby interleaving the various tristimulus primary color components toprovide the best image quality as empirically determined by actualvisual performance of such systems. As shown in FIG. 5B, the respectiveprimary colored light durations 300 a, 300 b, and 300 c are contiguouswith one another. However, provided a display system (for example, thedisplay disclosed in U.S. Pat. No. 5,319,491) is capable ofnoncontiguous primary color light sequencing, further possibilities formodifying and/or improving the visual quality of the video images beingtransduced by the display system can be marshaled. In this embodiment,the primary colored light a, b, c may be interleaved as illustrated inFIG. 5C so as to provide average potential intensity across the entireaggregate three-primary pulse duration of 1/60^(th) of a second. Thisdiffers from the effects of bit-splitting-based averaging disclosed inFIG. 4C, which is limited to gray scale generation within a singleprimary color, and does not involve the interleaving of bit weightsacross color boundaries such as is shown in FIG. 5C, where it should benoted that the suffixes refer to the three primaries (the most commonassociation would be a for red, b for green, and c for blue, so that 302b would represent the second most significant bit for the primary colorgreen). Note that the ordering of the bits in FIG. 5C no longer followsthe conventional sequence of red-green-blue, and so does not lend itselfto displays that are tied to sequential processing of the respectiveprimaries (such as obtains in the case of color-wheel-based illuminationsystems used in projection-based displays). In this instance, FIG. 5Csecures the benefits of the approach alluded to in FIG. 4C, except thatFIG. 5C employs coordinated manipulation of illumination intensity tothe display, the interleaving of the primary colors, and theimplementation of noncontiguous sequencing to insure maximum averagingof light energy for any given primary over the entire three-primaryduration of 1/60^(th) of a second, which was arbitrarily selected at theoutset as a reasonably nominal frame rate for a field sequential colordisplay system.

A fifth embodiment is a method that may include combining intensitymodulation with PWM to create hard-wired front-loaded bit weighting tofurther enhance perceived mitigation of motional artifacts using virtualaggregate pulse width truncation. The fifth embodiment of the presentdisclosure distributes conventional pulse-width-modulated temporalpulses so as to front-load all the most significant bits relative to thespecific single video frame being generated, with the lower order bitscontributing less information to the image being generated beingrelegated to the end of the aggregate tristimulus colored light pulsecomprising the entire color frame. By front-loading (or back-loading,which would be optically equivalent to the human eye: the benefit arisesfrom grouping the most important pulse of all colors as closely aspossible) the most important bits, the image undergoes virtualtruncation due to such temporal rearrangement of the pulses comprisingit. This embodiment hardwires the bit sequence from the most significantbits of all three primary colored lights being encoded first, followedby the next most significant bits of all three primary colored lights,and so on down to the least significant bits. Such virtual truncationcan serve to mitigate motional breakup artifacts without, in fact, trulytruncating the pulse in time, by means of such synchronous hardwiredweighting of the respective bits to be displayed. The bulk of theinformation comprising the important features of the frame are displayedfirst, and the less important features are displayed later in time (andare likely to represent lower image value portions of the display andthus will be more difficult to resolve at video speed causingundesirable artifacts to be less noticeable as a result).

As referenced in FIG. 5B, the unmodified method for implementingmultiple intensity levels in conjunction with pulse width modulation isshown without respect to the lower order bits which are ignored for thesake of visual and explanatory clarity. By already implementingintensity modulation, this fifth embodiment already enjoys some actualpulse width truncation as described for earlier embodiments where suchintensity modulation is taught herein. However, there are additionalperformance enhancements available that may be gained by introducing anew method to add virtual pulse width truncation. Virtual pulse widthtruncation involves the principles of visual perception, and exploitsthe fact that by rearranging the bits in an appropriate way, the bulk ofthe visual data comprising the important elements of a video frame willbe displayed close together in time, forming a tighter-packed ensembleof bit weights, while the lower order bit weights are postposited behindthe more significant bits and, being lower order bits, are (inprinciple) less visible, tending to cause whatever artifacts may ariseto be reduced in visual magnitude.

FIG. 5D illustrates the hard-wired interleaving of primaries to achievethe desired virtual pulse width modulation. Note that the highest orderbits referred to as the most significant bits 301 a, 301 b, and 301 cfor the three primary colored lights a, b, c are displayed first as afirst ensemble 501 comprising bits 301 a, 301 b, and 301 c. Thereafter,the second most significant bits 302 a, 302 b, 302 c are displayedsecond as a second ensemble 502, followed by a descending series of bitorders (i.e., third most significant bits 303 a, 303 b, 303 c aredisplayed third as a third ensemble 503, followed by the fourth mostsignificant bits 304 a, 304 b, 304 c displayed fourth as a fourthensemble 504). This sequence is termed hard-wired since it invariablydisplays the bit planes comprising the respective gray scaledecomposition of any given video frame according to this precisesequence. This sequence need not be synchronous (tied irrevocably to aclock) if some bit weights are not included in the program content, acircumstance which could lead to further temporal truncation. The bitweight order taught in FIG. 5D will tend to insure that the phenomenonof virtual pulse width truncation will occur for a majority of videoframes being processed by the display system. One advantage of thisapproach is that it requires no real time analysis of video content, byvirtue of being hard-wired as a method for encoding the data. Therefore,this fifth embodiment enjoys not only the benefits of actual aggregatepulse width truncation, it adds the benefits of virtual pulse widthtruncation to further reduce the appearance of possible visual artifactsrelated to field sequential color display system operation. Note, too,that the method illustrated in FIG. 5D can be applied even if intensitymodulation is not being applied, as previously illustrated in FIG. 3F.This embodiment of the present disclosure may also include any orderingof the bits within each of the ensembles 501, 502, 503, etc., shown inFIG. 5D, whether or not the flux is generated by a combination ofintensity and pulse width modulation, solely by pulse width modulation,or solely by intensity modulation, for example in ensemble 501 the bitsmay be any order such as 301 b, 301 c, 301 a. It should also be notedthat the precise position within the 1/60^(th) overall frame beingdisplayed for the most significant bits is not important, for example,while FIG. 5D suggests that the heaviest weighting (i.e., mostsignificant bits) occurs at the left, early in the aggregate pulse forall the bit weights to be displayed, the most significant bits couldjust have easily been situated at the right, and have thus beenback-loaded, with identical generation of the virtual pulse widthtruncation effect. Distribution of the heaviest weighting around thecenter of the 1/60^(th) of a second frame period would be of equalpotential value. The embodiment covers all such variations of theloading sequence, for which a point to be grasped for this method is anexplicit concentration of the most significant bits as close in time aspossible, regardless where within the frame pulse said concentration isto occur. The fact that FIG. 5D illustrates that this concentration isat the front of the pulse, at the left, is not material to theembodiment but only represents one possible (and convenient) approach.Wherever the concentration of the highest bits is positioned, it may behard-wired to always fall in that position insofar as this embodiment isconcerned.

A sixth embodiment is a method that may include combining intensitymodulation with PWM to create a real-time dynamically-determinedfront-loaded bit weighting to further enhance perceived mitigation ofmotional artifacts using virtual aggregate pulse width truncation. Thesixth embodiment of the present disclosure may apply the same generalvirtual truncation as the fifth embodiment does, and thereby also servesto mitigate motional breakup artifacts without, in fact, trulytruncating the pulse in time. This sixth embodiment is dependent uponreal-time evaluation of each frame being generated, because thedistribution and weighting of the bits is no longer hardwired andsynchronously fixed, but is determined in real time video frame by videoframe. The rearrangement of the bits to be displayed in this sixthembodiment must be calculated prior to generation of the frame foractual display to the viewer, which will likely require look-aheadcapability in the video cache to preprocess each frame in regard to therequired real-time analysis process. In contrast to the hardwired bitsequence of the fifth embodiment, the sixth embodiment dynamicallyadjusts the bit sequence in light of the exigencies of each frame'sprogram content, thereby insuring that the correct bits are trulyweighted to the front of the aggregate pulse being encoded across allprimary colored lights, which cannot always be guaranteed in the case ofthe hardwired fifth embodiment.

In regard to program material (video content), it is not always truethat the highest order bits contain the video information that definesthe key thresholds within a video image. The fifth embodiment,therefore, represents a very useful approximation and provides virtualaggregate pulse width truncation for about 75% or more of theinformation being displayed on a video system so equipped. But, for theremaining 25% of program content, the fifth embodiment may provide noapparent advantage or could even theoretically serve to extend ratherthan truncate the virtual perception of the pulse, therefore aggravatingrather than mitigating motional artifacts during the display of theaffected video frames.

This sixth embodiment discloses an alternative method for determiningthe best order in which to display the bit weights comprising a videoframe. Real-time video analysis software that is capable of calculatingthe visually significant gray scale levels in a full color frame at fulloperational speed can supply a display system with the means to re-orderthe bit weights on a frame-by-frame basis to insure that the bit weightsthat truly represent the most visually significant bits (not merely thebits that represent the largest arithmetic values) are displayed first.In most cases, these values are likely to match that for the hard-wiredfront-loaded bit weight encoding method disclosed in the fifthembodiment above, but any given frame may well deviate from thisstandard, as suggested in FIG. 5E, where the most visually significantbits 301 a, 302 b, 304 a (as contrasted to the conventional definitionof most significant bit as a purely mathematical definition) aredisplayed first in a first ensemble 506, followed by the next mostvisually significant bits 304 b, 304 c, 302 a displayed second in asecond ensemble 507, followed by the next most visually significant bits302 c, 303 a, 301 c displayed third in a third ensemble 508, followed bythe next most visually significant bits 301 b, 303 b, 303 c displayedfourth in ensemble 509 (e.g., the least most visually significant bitsin ensemble 509 for a 4-bit system as illustrated in FIG. 5E), etc. Notethat the constituent elements comprising the most visually significantbits 506 are clearly not the three most significant bits as theyappeared in FIG. 5D. Because the video content may involve objects ofone color moving against a background with a rather similar color, thedistinction between the object and its background is likely to bedetermined by bits other than the most significant bits mathematicallyconsidered, but rather by bits that define the shade of differencebetween object and background, which could readily be a lower order bit,as suggested by the composition of first ensemble 506 in FIG. 5E. Thesample provided in FIG. 5E gives an arbitrary example, forimplementation of this sixth embodiment would likely entail thecustomization of the bit weight sequence for every consecutive frame ofvideo being encoded by the display driver circuitry to provide bothmaximum actual aggregate pulse width truncation across all colors, plusmaximum virtual pulse width truncation due to front-loading of the mostvisually significant bits determined on a frame-by-frame basis by thesystem doing the video analysis and providing the driver circuitry thecorrect information to re-arrange the interleaving of the variousprimaries, their intensities, and their pulse widths to insure thedesired result as elaborated above.

A seventh embodiment is a method that may include the real-timequantizing/posterizing of foreground objects moving relative to theirbackground in a video frame sequence to gain actual and virtualaggregate pulse width truncation and concomitant mitigation of motionalartifacts associated with FSC displays. The seventh embodiment of thepresent disclosure may extend a method of the fifth and sixthembodiments to a more elaborate level to achieve further gains in therealm of motional artifact mitigation in field sequential colordisplays. This embodiment is a variant of the previous method andincludes determination (by intelligent real-time frame analysissoftware) of which portions of the image represent foreground objects insufficiently rapid motion against the background being displayed towarrant the imposition of artifact mitigation methods. Motionalartifacts are known to aggregate around such foreground objects at theirborders in the direction of motion across the display. The method callsfor the identified part of the frame that represents the movingforeground object to be converted, via an intelligent modulo method,into a reduced bit-depth image with the bits comprising the object beingtargeted for front-loading for the frame in question. For example, anairplane against a blue sky would be identified as a foreground movingobject by the video analysis software. Both airplane and blue sky areoriginally encoded as 24-bit color (8 bits per tristimulus primary). Therevised frame in this method would re-encode the airplane portion of theframe in a reduced bit-depth (e.g., 12-bit color, or 4 bits pertristimulus primary), and those moving-object-related bits for allrelevant tristimulus primary colors would be front-loaded and transducedfirst before processing the remaining 12-bits which define the sky'sgreater bit depth. Because the foreground object is in sufficientlyrapid motion, the loss of bit-depth is not apparent to the eye duringits transit across the display. This real-time dynamic bit-depthadjusting method is invoked only as needed based on program content tomitigate and/or prevent the onset of motional color artifacts.

This seventh embodiment is schematically illustrated in a flow chartdepicted in FIG. 6, which provides a method for preprocessing video datato be encoded using field sequential color pulse width modulationtechniques. The mitigation of motional artifacts may be applied tospecific regions of a video frame, those regions most likely to beaffected by artifacts by virtue of relative motion between that region(which thus represents a moving foreground object) and the background.Motional artifacts tend to occur at the borders of the foreground objectand appear as color smearing and decoupling in the direction of apparentmotion of the object. The principles that inhere in this method may alsobe adapted to situations where motional breakup is caused by relativemotion of the display screen with the viewer's head (such as might occurwith an avionics display when the pilot's cockpit is significantlyvibrating). In that instance, a desired preprocessing effect may beimposed on the entire display if vibration is detected by an appropriatesensor. In general use, however, the preprocessing effect under thismethod is applied to objects in the video frame sequence that areintelligently determined, via real-time video analysis, to be moving atsufficient speeds relative to their background as to cause a significantrisk for motional artifact generation and the resulting temporaldecoupling of the edges of the object being tracked by the observer'seyes.

By way of background, there are means in the prior art for determiningwhich parts of a video frame sequence represent an object in motion. Twomethods for conducting such real-time analysis have been put forward byZlokolica et al. (“Fuzzy logic recursive motion detection and denoisingof video sequences,”Journal of Electronic Imaging, April-June 2006/Vol.15(2), 023008-1ff) and by Argyriou and Vlachos (“Extrapolation-freearbitrary-shape motion estimation using phase correlation,” Journal ofElectronic Imaging, January-March 2006/Vol. 15(1), 010501-1ff).Therefore, the implementation of such a step within the method disclosedhereunder shall be understood to represent either one or the other ofsuch methods, a combination of them, or an equivalent or superiorapproach to that enunciated by these research teams, and as suchreflects an existing but growing body of knowledge in the field of imageanalysis, particularly in regard to video analysis. Because motiondetection under such systems requires several subsequent frames to beanalyzed at once, this embodiment presupposes the existence of asuitable video cache capable of feeding such a real-time analysis systemas might be assembled according to principles published by theresearchers alluded to above.

Further, this embodiment is based on selective posterization (orquantization) of the moving region(s), if any, in the video stream beinganalyzed. Posterization involves a deliberate reduction in the amount ofgray scales involved in depicting an image or a portion of an image.When a part of the video stream is detected to represent a foregroundobject moving rapidly with respect to the background, it may beadvantageous for that object to undergo both actual and virtualaggregate pulse width truncation to mitigate the artifacts that couldarise if the frame rates or blanking periods are not suitablyconfigured. One way to induce such truncation is to reconfigure themoving object in regard to the bit weights comprising it, so that it maybe represented by four or five bits rather than all eight bits of eachprimary color. This reduction in bit depth will cause a visual effectknown as posterization, wherein gentle gradations within the objectbecome more sharply defined and less smooth. Since the object is inrapid motion, this brief loss of gray scale depth is far lessobjectionable than motional color breakup artifacts are (which even tendto elongate the moving object in the direction of motion, which isunacceptable for display systems involved in training pilots insimulator systems where target acquisition is premised on accurateshapes for moving objects on-screen).

Therefore, by reducing the bit depth of the moving object andreconfiguring the display bit order for all primaries in light of thebasic principles incorporated in the sixth embodiment (and reflected inthe example given in FIG. 5E in which the most visually significant bitstake precedence over the mathematically most significant bits), aperformance improvement in regard to motional artifact mitigation can beenjoyed by the display incorporating this method.

Referring to FIG. 6, incoming video signal 601 is received in the videocache 602 that is used to feed data in appropriate incrementsframe-by-frame to the real-time motion analysis subsystem 603, a systemsuch as was alluded to above in regard to the prior art in the field ofreal-time image analysis applied to video streams. Several frames areprocessed at once by the analyzer 603 to determine the status, intemporal context, of the first frame being processed. The system thendetermines 604 whether or not there is any relative motion between oneor more foreground objects and the apparent background, and whether ornot the motion is sufficiently rapid as to be likely to cause motionalcolor breakup artifacts. If there is such relative motion, then thedefined region(s) of the video frame that are detected to be in rapidrelative motion are resampled/posterized/quantized 605 so as tointelligently reduce the number of gray scales defining the region(s)detected to be in motion (and thus representing moving objects againstthe displayed background in the video frame). The bit sequence forencoding may also be adjusted in real-time if the principles of thesixth embodiment are being followed in the device, otherwise not. Ifthere was no detected relative motion, then the video frame is notposterized or resampled but is passed on as-is to the primary encodingengine 606. If there was indeed such motion, the parameters for thevideo adjustment are handled at the analyzer 605 and anyencoding-specific adjustments (if the sixth embodiment is alsoimplemented) are passed as determinative parameters to the encodingengine 606 which then determines the order of the bits to be displayedacross all three primary colors.

The video frame, whether or not it has undergone real-time selectivedynamic posterization at 605, is displayed at 607; the video cache isqueried 608 to determine if it is empty. If it is, information displaywould naturally cease 610; if there are more frames to process, then thesystem increments 609 such that sufficient video frames are present inthe cache 602 to insure that the real time motion analysis system 603can continue to correctly determine whether the frames in contextexhibit sufficient relative motion within the program content to triggerthe posterization step 605.

The posterization step may involve any number of rounding methods tosecure the desired result. One example of such a method is disclosed in“Adaptive color quantization using the baker's transformation,” byMontagne et al., Journal of Electronic Imaging, April-June 2006, Vol.15(2), 023015-1ff), however there are a host of methods for securinguseful results. The purpose of the posterization step is to providefurther gains in artifact mitigation by reducing the system overheadrequired for generating the full gray scale bit depth for the movingobject. Instead of, for example, the object (which may be an aircraftbeing displayed against a blue sky) being displayed in 24-bit color, itmay be displayed in 12-bit color if it is moving rapidly against the skyin the video sequence. The combination of the sixth and seventhembodiments herein will provide maximum actual and virtual truncation ofthe aggregate color pulses that generate these images.

It should be understood that the methods outlined here are not limitedto the three tristimulus primaries but may be applied to extended gamutscenarios where additional visible primary colored light(s) are used toencode video data. The methods outlined here may also be applied to theinterleaving of nonvisible primaries (e.g., infrared light) with visibleprimaries as well, and is not restricted in any way to the threewell-known tristimulus primaries (e.g., red-green-blue). The samemethods for intensity modulation coordinated with pulse width modulationand the other methods disclosed apply to all such display systems.

It will be seen by those skilled in the art that many embodiments takinga variety of specific forms and reflecting changes, substitutions, andalternations can be made without departing from the spirit and scope ofthe invention. Therefore, the described embodiments illustrate but donot restrict the scope of the claims.

The invention claimed is:
 1. A method comprising: displaying a video image using field sequential color encoded in a plurality of video frames; receiving the plurality of video frames for displaying a foreground object and a background image in the video image; determining in the received plurality of video frames that the foreground object of a video image of at least one of the video frames is in motion relative to the background image of the video image; modifying a gray scale of the at least one of the video frames associated with the foreground object that is in motion relative to the background image of the video image to reduce the number of gray scales defining the foreground object; encoding the plurality of video frames including the modified video frame for image generation; and displaying the encoded plurality of video frames, including the modified video frame.
 2. A method for removing field sequential color artifacts that arise in a display system that temporally segregates color components of a video image and presents each frame of video information by rapid consecutive generation of each color component when the color components of the video image making up a composite frame of video information do not all reach a same region of an observer's retina due to relative motion of the retina and the video image to be displayed, the method comprising: receiving a video signal for displaying the video image comprising a foreground object and a background image, the video signal further comprising a plurality of video frames, each video frame comprising a plurality of bits representing a gray scale of one of a plurality of the color components used by the display system to display the video image; determining that the foreground object is moving relative to the background image; and modifying a video frame containing color gray scale information associated with display of the foreground object to reduce the number of gray scales defining the foreground object.
 3. A display system comprising: a display panel for displaying a video image using field sequential color encoded in a plurality of video frames; a video cache for receiving the plurality of video frames for determining whether the foreground object is moving relative to the background image; a motion analyzer processing the plurality of video frames for determining whether the foreground object is moving relative to the background image; the motion analyzer determining the foreground object is moving relative to the background image and further comprising circuitry for modifying a gray scale of the foreground object of at least one of the plurality of video frames in response thereto to reduce the number of gray scales defining the foreground object in the at least one of the plurality of video frames; an encoder for encoding the plurality of video frames including the modified video frame for image generation; and displaying the encoded plurality of video frames, including the modified video frame. 